This disclosure relates to dry adhesives, methods of manufacture thereof and articles comprising the same.
It is generally known that as signal line frequencies increase, a larger portion of the electrical signal propagates along the outer periphery of the conductor (a phenomenon known as the “skin effect”). Copper foils used in the fabrication of printed circuit boards are surface treated in order to enhance peel strength to the laminate as well as to passivate the highly reactive surface of the copper. Mechanical modification of the surface caused by the surface treatment results in increased surface roughness, which promotes signal loss at high frequencies. In addition, the chemical treatment of the surface causes the formation of less electrically conductive alloys on the surface of the copper foil, which generally causes increases in resistivity and additional signal losses. Therefore, from an electrical perspective, it is desirable to use the smoothest copper foil available.
Unfortunately, very smooth copper foils exhibit reduced peel strength when bonded to a polymeric material that is used in a laminate. In other words, the smooth copper foils can be easily detached from a layer of polymeric material thus causing destruction of the laminate. In an effort to address this concern, foil manufacturers employ a primer or B-staged polymeric polymer that is compatible with the low loss laminate matrix. However, no one primer is sufficient for every laminate matrix. For example, a primer utilized for a laminate that comprises an epoxy or epoxy/cyanate ester that has a high glass transition temperature is ineffective for use in laminates that comprise a polyphenylene ether. Consequently, a plurality of primers and associated additional processes are used for the various commercially available polymeric materials that are used to form laminates. Using a primer thus increases manufacturing cycle time and increases the cost of the laminate. It is therefore desirable to provide a single adhesive solution to the peel strength issue currently plaguing smooth copper foils.